The invention relates to the field of detecting failures of mechanical elements in a fluid flow regulator system for a fluid-passing duct in a turbine engine. More precisely, the invention relates to a method of testing integrity in a fluid flow regulator system for a turbine engine.
A particular application of such a fluid flow regulator system, when the fluid is air bled from an air passage in the turbine engine, relates to managing the radial clearance between a rotor and a stator of a turbine in the turbine engine, e.g. between rotor blades and a stator ring surrounding the blades. This management is particularly important for controlling the performance of the turbine engine, in particular for controlling its efficiency and its maximum thrust. In order to control this radial clearance, it is known to make use of a circuit for cooling the stator by bleeding air from the flow passage for the secondary stream through a bypass turbine engine. Advantageously, the rate at which air is bled from the air stream is regulated and, by cooling the stator, it serves to control expansion of the stator, and thus to control its radial clearance relative to the rotor.
For a bypass turbine engine, a first known method consists in using a scoop to act passively to bleed off a portion of the air stream in the flow passage for the secondary stream, and then to regulate the flow rate of the air stream that has been bled off by means of a flow regulator valve inserted in the air bleed circuit. By way of example, one such solution is described in Document FR 2 614 073. The main drawback of that solution lies in the fact that installing an open scoop in the flow passage for the secondary stream gives rise to large head losses.
In order to mitigate that problem, and thereby improve the performance of the turbine engine, it is known to form a scoop in a services-passing arm that extends across the flow passage of the secondary stream, with the scoop then bleeding off an air stream actively from the flow passage for the secondary stream. Under such circumstances, the scoop is active in the sense that it is associated with a flap that is pivotable between an open position and a closed position, thereby enabling the flow rate of air that enters the scoop to be regulated as a function of the position of the flap. By way of example, one such solution is described in Document FR 3 025 843.
The movable flap of that scoop is commonly opened using an actuation force that results from moving a drive rod of an actuator. The actuation force is transmitted to the movable flap via a push-pull cable, thereby serving to control movement of the movable flap. The actuation rod is moved when the actuator is powered, the power supply to the actuator being controlled by an electronic computer. In the event of the computer detecting a problem, it can then cause the power supply to the actuator to be stopped, thereby stopping any opening of the movable flap of the scoop.
Furthermore, the scoop includes safety return means in the form of a spring serving, in the absence of any actuation force being transmitted by the cable to the movable flap, to bring the movable flap into its closed position, which position corresponds to a safe position for the movable flap of the scoop, commonly referred to as its “fail-safe” position.
For reasons of accessibility, in particular concerning temperature, the electronic computer uses closed loop regulation only for the movement of the drive rod of the electrical actuator. Such regulation is performed on the basis of measurements delivered by a position sensor that measures the successive positions of the drive rod of the actuator. The opening of the movable flap of the scoop is then correlated by the electronic computer as a function of the position of the drive rod of the actuator.
A major drawback involved in implementing such a solution then occurs whenever there is a break in the safety return spring or in the cable making the connection between the drive rod of the actuator and the movable flap. If it is the spring that breaks, it is no longer possible to ensure that the movable flap of the scoop will take up its fail-safe position in the event of a failure of the power supply to the actuator. If it is the cable that breaks, the actuator can no longer transmit its actuation force to the movable flap and thereby open it.
In the above-mentioned situations, the drive rod of the actuator nevertheless continues to be movable and its movement continues to be measurable by the position sensor. Since the physical states of the cable and of the safety spring are not supervised by the electronic computer, it can therefore not detect that the spring or the push-pull cable has broken, and consequently it will assume that the operation of the air flow regulator system is nominal, even when that is not so.
Such situations are therefore dormant. In addition, their impact cannot be observed in the short term on the engine itself. Specifically, it is then difficult to observe degraded performance or wear in mechanical parts. Consequently, breakage of the spring or of the push-pull cable can remain dormant during a large number of cycles and, in the longer term, can lead to irreversible degradation of the engine, e.g. excessive wear of abradable surfaces or a reduction in the lifetime of the casing of the low-pressure turbine.
An analysis of failure trees in order to identify the cause of such degradations cannot allow the presence of dormant contributors, particularly if such failures may occur at a potentially large rate. Specifically, the persistence of dormancy for the above-mentioned failures greatly limits the viability of air flow regulator systems that make use of scoops of that type.